Ambient Particulate Matter Monitoring - A Case Study at Tarkwa

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1 Research Journal of Environmental and Earth Sciences (): -, 0 ISSN: 0-0 Maxwell Scientific Organization, 0 Submitted: December, 0 Accepted: January 0, 0 Published: April, 0 Ambient Particulate Matter Monitoring - A ase Study at Tarkwa Kenneth J. Bansah and Newton Amegbey Mining Engineering Department, University of Mines and Technology, Tarkwa, Ghana Abstract: Air pollution from airborne particulates remains a major concern of the communities within the mining areas. In Ghana, little research has been done to ascertain the health implications of living around the mine sites. This study studied ambient particulate matter less than 0 :m (PM0) pollution at Gold Fields Ghana Limited (GFGL) mine residence in Tarkwa. A four-month PM0 monitoring was performed at GFGL mine residence. The Gaussian Dispersion Model was also used to predict the concentration of PM0 in the Tarkwa Township. The results show that % of the PM0 concentrations obtained exceeded the Ghana Environmental Protection Agency s threshold limit of 0 :g/m. The dispersion model indicated that PM0 generated from GFGL attains a concentration of :g/m when it reaches the Tarkwa Township. Key words: Airborne particulates, air pollution, health implications, tarkwa, threshold limit INTRODUTION Air pollution from airborne particulates is a major concern of the communities within the mining areas. Gold Fields Ghana Limited (GFGL), Tarkwa, Ghana operates an open pit mine. The mining activities involve overburden removal, drilling, blasting, loading, hauling and ore crushing. These activities together with increased vehicular movements on the untarred roads within and around the mine sites introduce particulates into the atmosphere. Particulates, when inhaled can evade the system s natural defences and lodge deep in the lungs, leading to lung and heart diseases. Zinatunor (), researched into pollution of ambient air by particulate matter less than 0 :m (PM0) at the Tarkwa Township in Ghana. During the period, a six-month data was collected. The results show that 0% of the PM0 concentrations obtained exceeded the Environmental Protection Agency of Ghana (EPA) threshold of 0 :g/m. A conclusion drawn was that mining activities in Tarkwa pose a serious particulate pollution threat to the Tarkwa Township. Amegbey and Ndur (000) concluded that surface mining activities around the Tarkwa town have contributed to increased air borne particulate matter within the township. It also recommended that further studies into particle pollution in Tarkwa must be carried out. The studies must include dispersion modeling and particulate analysis in order to determine the sources contributing to the dust levels in the Tarkwa Township. In trying to solve particle pollution due to mining, in the Tarkwa Township, Gold Fields Ghana Limited (GFGL) residence which is most likely to be affected was selected as the study area. This study therefore, looks at PM0 levels and the possible impacts on residents at Gold Fields Ghana Limited mine site and the Tarkwa Township as a whole. Location, relief, topography and climate of GFGL: Gold Fields Ghana Limited, Tarkwa Mine, is located off the Tarkwa-Bogoso highway, about. km from Tarkwa in the Western Region of Ghana. Tarkwa Township has a population of about 00. The topography of the mine comprises of ragged ridges with peaks reaching a height of m above mean sea level in some areas, interspersed by undulating valley bottoms and a true reflection of the pitching fold structures of the Banket Series of the Tarkwaian System. Elevation in the area ranges from approximately 0 to m. The central area of the mine is low lying and flatter and does not show the variations in elevation typical of the south and eastern areas near Tarkwa and Akontansi (Akurang, 00). The mining area falls within the western equatorial climatic zone, with seasons primarily regulated by moist, south-west monsoon winds from the South Atlantic Ocean and dry dust-laden north-east trade winds, known as Harmattan, which blows over the Sahara Desert from the northern sub-tropical high pressure zone. The inter Tropical onvergence Zone crosses the mining area two times per year, causing hydrometeorological data including rainfall to peak during two periods; April to June and October to November. The mean annual rainfall is approximately mm; with a range of 00 to 00 mm. Average monthly temperatures range between and, with the highest orresponding Author: Kenneth J. Bansah, Mining Engineering Department University of Mines and Technology, Tarkwa, Ghana

2 Res. J. Environ. Earth. Sci., (): -, 0 oncentration ( g/m ) oncentration ( g/m ) oncentration ( g/m ) 0 -feb-0 0-feb-0 -feb Mar-0 -Mar-0 -Mar-0 -Mar-0 -Mar-0 -Apr-0 -Apr-0 -Apr-0 -Apr-0 -Apr-0 -Apr-0 oncentration ( g/m ) -feb-0 -feb-0 -feb-0 -feb-0 -feb-0 -feb-0 oncentration ( g/m ) -Mar-0 -Mar-0 -Mar-0 -Mar-0 -Mar-0 -Mar-0 oncentration ( g/m ) -Apr-0 -Apr-0 -Apr-0 -Apr-0 -Apr-0 -Apr-0 -Apr-0 -Apr-0 -Mar-0 -feb-0 -feb-0 Fig. : PM0 concentration profile for February 00 -Mar-0 -Mar-0 Fig. : PM0 concentration profile for March 00 Fig. : PM0 concentration profile for April 00 -Mar-0 -Apr-0 temperatures recorded during February and March. Annual evaporation is much less than the annual precipitation, although evaporation losses from surface water bodies can be significant during the few dry months of the year (Akurang, 00). PM0 monitoring and results: A h PM0 monitoring was conducted for 0 days at GFGL residence. The monitoring activity started from the th of February and ended on the th of June 00. This period was mainly oncentration ( g/m ) 0 -May-0 -May-0 -May-0 -May-0 oncentration ( g/m ) 0-May-0 -May-0 -May-0 -May-0 -May-0 0-May-0 -May-0 -May-0 -May-0 Fig. : PM0 concentration profile for May 00 -May-0 0-May-0 characterized by dry weather conditions, although there were few millimeters of rain. In all, 0 PM0 data were collected using the PQ00 Air Sampler. Five of the samples were discarded due to mishandling and moistening of the filter membranes. The procedure adopted for the particulate sampling with the PQ00 Air Sampler is as follows: A mm Whatman filter is weighed with a microbalance in a temperature and humidity controlled filter weighing room and inserted in the filter cassette. The weighed filter is placed in the PQ00 Air Sampler filtering unit. With a flow rate of. Lpm, the pump of the PQ00 is set to run for h. The filter with the particulate sample is removed from the system and weighed after the h sampling duration. The contaminant weight is determined by the difference between the post and pre-sampling filter weights. With the contaminant weight, the sampling duration and flow rate, the concentration of the particulate is determined according to Eq. (): oncentration(:g/m ) = ontaminants Weight () (mg) 000/ Total Sample Volume (m ) ontaminant weight is the difference between initial filter weight and final filter weight in milligrams, and Total sample volume is the volume of air passed through the filter in cubic meters. The PM0 concentrations obtained during the period under review were plotted to determine whether these concentrations exceeded the EPA guideline value. Figure,, and illustrate the monthly variations in PM0 concentrations at GFGL. While the maximum PM0 concentration was 0 :g/m, the minimum concentration

3 Res. J. Environ. Earth. Sci., (): -, value Geometric mean 0.0 oncentration ( g/m ) Probability Fig. : Probability versus mass concentration was. :g/m. These concentrations were respectively recorded on and th April, 00. The average PM0 concentration over the period of study was calculated to be :g/m. The PM0 concentrations were further grouped into concentration ranges. The probability that a given concentration will not be exceeded was calculated. A graph of these probabilities versus the upper class limit values of the concentration range was plotted on a logprobability graph paper (Fig. ). From the graph, the probability that a given concentration will fall below the EPA guideline value is read to be %. Thus the probability of obtaining a concentration higher than the EPA guideline value is %. The geometric mean is also read to be 0 :g/m. z PM0 modeling and results: The Gaussian Dispersion Model was used to predict the concentration of PM0 in the Tarkwa Township. The Model is given by Eq. () (ooper and Alley, 00): Q H exp y z z () where: = steady-state concentration at a point (x, y, z), :g/m Q F y, F z = Emissions rate, µg/s = Horizontal and vertical spread parameters respectively, m µ = Average wind speed at stack height, m/s y = Horizontal distance from plume centerline, m oncentration ( g/m ) Tarkwa Distance (km) Fig. : Distances versus PM0 concentrations = Vertical distance from ground level, m H = Effective stack height, m With a stack height of 0 m at the processing plant and m (assumed) for each of all other particulates emission sources, the effective stack height (H) was calculated to be. m. This is as a result of the assumption that 0% of the emissions come from the processing plant while 0% come from other sources. Other parameters include a wind speed (:) of 0. m/s, emission rate (Q) of 0 :g/s and a slightly stable atmosphere. Modeling was performed over a distance up to about km. The result of the modeling is illustrated in Fig.. DISUSSION The minimum and maximum concentrations were. and 0 :g/m, respectively. While for % of the time

4 Res. J. Environ. Earth. Sci., (): -, 0 Fig. : Relative positions of gold fields Ghana limited and tarkwa township concentrations fell below the threshold limit value (TLV) of 0 :g/m set by the Environmental Protection Agency of Ghana, for % of the period of measurement particulates concentration exceeded the EPA limit. Data available from February to May indicates an average PM0 concentration of :g/m in the Tarkwa Township (Zinatunor, ). However, during the period under review, the average concentration was 0 :g/m. This reduction in PM0 concentration may be due to increase dust suppression activities by GFGL. Moreover, most of the roads within and around the Tarkwa Township currently, have been tarred. It is interesting to note also that the highest PM0 concentration of 0 :g/m was recorded only once, during the period of study. This single highest concentration is lower compared to the average PM0 concentration in. The results of particulates modeling show that PM0 concentration exceeded the 0 :g/m threshold set by EPA, within a distance of about. km from the mine. Also, PM0 generated from GFGL attains a concentration of :g/m when it reaches the Tarkwa Township. As expected, the concentration of PM0 decreased as the distance of transportation increased (Fig. ). This occurs due to the fact that, as particulates are transported, they come into contact with each other, coagulate and fall by gravity. Some particles may also react with other substances to form secondary particulates, which can get deposited by dry or wet deposition. Others may adhere themselves to water droplets, increasing their aerodynamic diameters as well as their settling velocity. An increase in wind speed will also cause dilution of PM0. Figure shows the relative positions of GFGL and Tarkwa. A wind rose with predominant wind direction of North-East over the study period has also been superimposed on Fig.. onventionally, a wind rose shows the various directions from which the wind blows. However, for easy interpretation of Fig., the superimposed wind rose indicates the directions to which the wind blows. It could be seen from Fig. that particulates emitted from GFGL can be transported by the wind towards the Tarkwa Township. ONLUSION Analysis of data collected and subsequent study of the results obtained, revealed that PM0 levels at Gold Fields Ghana Limited mine residence exceeded the Environmental Protection Agency s threshold limit of 0 :g/m, % of the time. Particulates emitted from GFGL attain a concentration of about :g/m on reaching the Tarkwa Township. AKNOWLEDGMENT The authors wish to acknowledge the support of Mr. Steve Gyan and all the staff of the Environmental Department of GoldFields Ghana Limited who contributed to the success of this research. REFERENES Akurang, J., 00. A Study of the Drilling and Blasting Practices at Goldfields Ghana Ltd. BSc. Project Report, (Unpublished), University of Mines and Technology, Tarkwa, Ghana, pp: -.

5 Res. J. Environ. Earth. Sci., (): -, 0 Amegbey, N. and S. Ndur, 000. Air Particulate Matter Monitoring in a Major Ghanaian Town. The ase Study of Tarkwa. Environmental Issues and Management of Waste in Energy and Mineral Production, Singhal and Mehrotra (Eds.), Balkema, Rotterdam, pp: 0. ooper,.d. and F.. Alley, 00. Air Pollution ontrol, a Design Approach. rd Edn., Waveland Press, Inc. Long Grove, Illinois, pp:. Zinatunor, K.,. Ambient air particulate matter monitoring in the tarkwa township. Ph.D. Thesis, Report, (Unpublished), Tarkwa School of Mines, Tarkwa, Ghana, pp:.